What is the connection between the modern horror genre and ancient Greek tragedy?

Notice that the ancient version of the theatrical masks of tragedy and comedy (see the Roman mosaic) did not portray simple frowning and smiling faces--as though the contrast were as simple as "sad versus happy."

No, the original form of these masks showed a grisly grimace for comedy, and for tragedy: a face not of anguished loss but of awesome shock and horror! These are much more complex character commentaries, not simple mono-emotions.

Further, tragedy and comedy are not two strictly separate kinds of story, but two psychological principles which mix together--which is exactly what happens in The Can Opener.

The philosophical nature of horror is not just to scare people for thrills, but to shock them into a full realization of some truth that we all sense but have not directly faced, perhaps because it is uncomfortable....